Methods and apparatus for the heating of animal tissue containing benign and malignant tumors and lesions without any apparent effect on the surrounding non-tumor tissue while necrosing or at least partially destroying the tumor mass are disclosed by LeVeen et al, JAMA 235:2198-2200(1976). An example of this is copending LeVeen patent application Ser. No. 643,661, filed Dec. 23, 1975, which describes the use of an R.F. generator attached to a single pair of electrode plates or discs which are placed in contact with the skin surface of the animal so that the submerged tumor mass is positioned in a field of R.F. energy set up between the pair of electrode plates. This apparatus works well, particularly with tumors which are near the surface and where high input of energy does not begin to pose a problem of skin surface heating and skin burn or irritation at the portal of entry of the energy.
However, in cases where a high level of energy is required over a longer period of treatment, up to several hours in some cases, a need for an apparatus which would maintain a constant level of R.F. energy input on the tumor target while at the same time reducing the surface tissue stress at the locus of contact between the skin of the patient and the electrode arose. This need was met by the design and manufacture of the hereinbelow described apparatus which comprises a plurality of sets of paired electrode plates. Each set of paired plates, i.e., applicators, are placed parallel to each other along an axis extending through the target tumor mass, but the sets are aligned on different axes, such that the portals of entry, the surfaces of the body against which the plates are positioned, differ. The various axes of paired plates of course intersect at the tumor mass within the body. The various sets of paired plates placed opposite each other operate under a timer control mechanism such that when R.F. energy is applied to one set of paired opposed electrode plates, the other sets of paired opposed electrodes are unenergized and inactive. When the first active set of electrodes is shut off by the timer, the next set automatically is activated and so on in sequence through the remaining sets of paired plates, activating one set at a time. In the preferred arrangement the length of time of actuation of each set of paired plates is controlled independently of the other sets, for example, by the provision of individual timing means associated with each set of paired plates through the control mechanism.